FILLING AND EMPTYING OF THE STOMACH:
HOW DOES IT WORK?

Filling of the stomach

Usually, people imagine the stomach as a dilated pouch where the food falls down. Consequently, it is often thought that the capacity of the stomach is related to the volume of the meals; feeding dryfood would make it “ shrink ”, because it is not very bulky. But it is a false belief. When empty, the stomach is flattened. The walls of the stomach are joined side by side because of the pressure exerted by the other organs. There is only an air pocket left in the upper area. The empty stomach is characterized by folds who disappear during the food ingestion.

During fasting, every 12 - 15 seconds, some electric waves run down the walls of the stomach, which maintains the tone up. When the dog eats, the tonic activity is inhibited and the body of the stomach can distend itself. It is called “ receptive relaxation ”. Thanks to this nervous activity of the stomach’s walls, the food accumulates but the internal pressure does not increase much.

Scheme of the dog’s stomach (longitudinal section)

Setting off of the stomach’s emptying

Stomach emptying only starts when the content has been sufficiently crushed and mixed to the gastric secretions, to be transformed into an assimilable mash for the intestine, called chyme.
Stomach’s emptying starts 15 to 60 mn after ingestion. It works very slowly, and it is not at all like a “ flushing effect ”. Total emptying lasts between 5 and 10 hours for a solid meal, but more than half of the content is evacuated around 3 hours after ingestion. This is not the initial volume of the meal that induces the speed of the stomach emptying.

Evolution of the gastric emptying percentage according to the time,
after ingestion of a solid meal
(from Gautier, 1997)

Influence of the particles size on gastric emptying
The particles obtained through gastric digestion have to be smaller than 2 mm to be able to pass through the sphincter located at the way out of the stomach, the pylorus.

Influence of the composition of the chyme on gastric emptying
During gastric digestion, small quantities of gastric content pass through the pylorus to be “ analyzed ” in the duodenum, which is the first part of the small intestine after the stomach. Actually, some receptors are located in the duodenum that are able to detect the amounts of fat, proteins and the quantity of available energy. So, this is the duodenum that regulates the chyme flow through the pylorus. When dogs receive liquid meals containing various quantities of glucose, the time of gastric retention varies in order to supply regularly about 1 kcal/mn to the duodenum, whatever the analysis of the diet is.

Conclusion

Whether a dog receive canned food or dryfood, the rythm of gastric emptying does not change much. However, rehydration of dryfood accelerates slightly gastric emptying. But the flow depends mainly on the energy content of the food. The best way to shorten gastric emptying is to divide the daily ration in several meals.